Ferritic stainless steel

ABSTRACT

A ferritic-type stainless steel suitable for manufacture into sheet and strip form that can be used for production operations involving stamping, punching, piercing, blanking and drawing by high-speed press production.

United States Patent I nvcntor Wesley Kalita New Kenslngton, Pa.

Appl. No. 802,631

Filed Feb. 26, 1969 Patented Sept. 21, 1971 Assignee Allegheny Ludlum Steel Corporation Pittsburgh, Pa.

F ERRITIC STAINLESS STEEL 5 Claims, No Drawings U.S. Cl 75/124, 75/ 126 D Int. Cl ..C22c 37/10, C220 39/14 Field of Search 75/124,

Primary ExaminerHyland Bizot I AttorneysRichard S. Speer and Vincent G. Gioia" ABSTRACT: A ferritic-type stainless steel suitable for manufacture into sheet and strip form that can be used for production operations involving stamping, punching, piercing, blanking and drawing by high-speed press production.

FERRITIC STAINLESS STEEL A number of existing ferritic stainless steels, while possessing adequate corrosion resistance in mildly corrosive media, suffer from relatively poor fabrication characteristics due to surface and subsurface titanium stringers. Typical of these alloys which contain titanium are AlSl type 409, type 499, and the commercial stainless steel known as MF-l produced and developed by Allegheny Ludlum Steel Corporation. The titanium stringers which may occur in these alloys are a source of breakage during forming and may be responsible for excessive die wear due to their abrasiveness.

The present invention provides a ferritic stainless steel of relatively low cost and adequate corrosion resistance but which is relatively free of harmful titanium stringers and particles. Alloys in accordance with the invention are particularly useful for replacement of brass, copper, aluminum and carbon steel fabricated articles in applications where moderate corrosion resistance is required and where fabrication includes a processing by high-speed punching presses which typically involve stamping, punching, piercing, blanking and drawing. 11- lustrative of the potential uses of alloys in accordance with the invention are in the manufacture of shotgun cases and automotive water pump seals. An additional advantage of steels I in accordance with the invention is their ability to be bright annealed and produce pickled finishes with good solid surface capable of withstanding the aforementioned fabricating operations. Compositions of the invention possess tensile properties as follows:

Tensile 60-70,000 p.s.i. Yield 3040.000 p.s.i. Elongation 23-35% Rockwell 8" 70 75 1n accordance with the invention there is provided a ferritic stainless steel consisting essentially of about up to 0.06 percent carbon, 0.2 to 1.0 percent manganese, to l 1.5 percent chromium, preferably 10.7 to 1 1.3 percent chromium, 0.2 to 1 percent silicon, preferably 0.2 to 0.5 percent silicon, 0.15 to 0.3 percent aluminum, 0.01 to 0.1 percent titanium, preferably 0.05 to 0.1 percent titanium, and the balance essentially iron with usual steelmaking residuals. The carbon content is limited because additional amounts beyond about 0.06 percent may result in a steel which is somewhat difficult to weld due to the formation of more martensite. The upper limits of the alloy contents of manganese and chromium are restricted to avoid developing unnecessary hardness and strength which would interfere with formability. At least about 10 percent chromium is, however, necessary for adequate corrosion resistance. The manganese and aluminum contents must be controlled to facilitate hot rolling. The aluminum limits of 0.15 to 0.3 percent are established to provide adequate weldability which is reduced if less than about 0.15 percent aluminum is included and to assure adequate ductility and formability which may be reduced if too much aluminum, e.g. more than 0.3 percent aluminum, is present. Titanium is included in amounts of at least 0.1 percent to improve formaare avoided to minimize stringer formation which, as mentioned previously, has an undesirable effect on stamping die wear.

' bility, however, amounts of titanium greater than 0.1 percent 4 As an illustration of the practice of the invention, three hotrolled coils of the composition described in table 1 were produced for processing into cold-rolled strip.

The coils were boxed annealed, wheelabrated and edge trimmed and thereafter cold rolled to 0.023 inch, 0.020 inch and 0.015 inch thicknesses respectively. Following cold rolling one-half of each coil was bright annealed and one-half annealed and pickled. The coils were then slit to width as required.

Table 1 below summarizes the transverse mechanical properties of the material produced. in addition, micrographic analysts of the material in the fully annealed condition confirmed the absence of large titanium stringer-type inclusions which would be detrimental to die wear.

TABLE 1 Nominal (Strip) Broad Range Chemistry Cheek Analysis Carbon up to 0.061 0.06 max. 0.056 Manganese 0.2 to 1.0% 0.30/0.50 0.38 Phosphorous 0.03 max. 0.024 Sulfur 0.03 max. 0.01 1 Silicon 0.2 to 1% 025/050 0.27 Chromium 10 to 11.5% 10.7/11.3 10.93 Nickel 0.30 max. 0.20 Aluminum 0.15 to 0.37: 0.15/0.30 0.26 Titanium 0.01 to 0.1% 0.05/0.10 0.10

Residuals Mol 0.065 Cu 0.12 N, 0025 TRANSVERSE MECHANICAL PROPERTIES Mechanical properties of cold r01 material After furnace an- Typical healing at 1,550 mechanical F. for five (5) properties minutes Yield, p.s.l 30/40, 000 33, 000 Tenslle, p.s.l 60/70, 000 64, 000 Elongation in 2', percent 25/35 30. 5 Rockwell B" /75 1 301 53 I Converted B" 55.

While several embodiments of my invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the appended claims.

Iclaim:

l. A ferritic stainless steel consisting essentially of about up to 0.06 percent carbon, 0.02 to 1.0 percent manganese, 10 to 11.5 percent chromium, 0.2 to 1 percent silicon, 0.15 to 0.3 percent aluminum, 0.01 to 0.1 percent titanium, and the balance essentially iron with usual steelmaking residuals.

2. A ferritic stainless steel according to claim 1 having 10.7 to 1 1.3 percent chromium.

3. A ferritic stainless steel according to claim 1 having 0.2 to 0.5 percent silicon.

4. A ferritic stainless steel according to claim 1 having 0.05 to 0.1 percent titanium.

5. A ferritic stainless steel according to claim 1 having 0.3 to 0.5 percent manganese. 

2. A ferritic stainless steel according to claim 1 having 10.7 to 11.3 percent chromium.
 3. A ferritic stainless steel according to claim 1 having 0.2 to 0.5 percent silicon.
 4. A ferritic stainless steel according to claim 1 having 0.05 to 0.1 percent titanium.
 5. A ferritic stainless steel according to claim 1 having 0.3 to 0.5 percent manganese. 